1. Field of the Invention
The invention relates generally to audio amplification systems, and more particularly to systems and methods for converting input data streams having a first sample rate to output data streams having a second data rate.
2. Related Art
Pulse Width Modulation (PWM) or Class D signal amplification technology has existed for a number of years. PWM technology has become more popular with the proliferation of Switched Mode Power Supplies (SMPS). Since this technology emerged, there has been an increased interest in applying PWM techniques in signal amplification applications as a result of the significant efficiency improvement that can be realized through the use of Class D power output topology instead of the legacy (linear Class AB) power output topology.
Early attempts to develop signal amplification applications utilized the same approach to amplification that was being used in the early SMPS. More particularly, these attempts utilized analog modulation schemes that resulted in very low performance applications. These applications were very complex and costly to implement. Consequently, these solutions were not widely accepted. Prior art analog implementations of Class D technology have therefore been unable to displace legacy Class AB amplifiers in mainstream amplifier applications.
Recently, digital PWM modulation schemes have surfaced. These schemes use Sigma-Delta modulation techniques to generate the PWM signals used in the newer digital Class D implementations. These digital PWM schemes, however, did little to offset the major barriers to integration of PWM modulators into the total amplifier solution. Class D technology has therefore continued to be unable to displace legacy Class AB amplifiers in mainstream applications.
There are a number of problems with existing digital PWM modulation schemes. One of the problems is that the performance and quality characteristics of the remainder of the signal processing system vary with the application. The exact implementation of the total system solution and the end-user application is not deterministic. As a result, implementation details cannot be accounted for apriori. Because existing technologies require application-specific solutions, they typically are not flexible, scalable or transportable to other applications. Consequently, these technologies generally are not applicable to mainstream systems.
One area in particular where existing digital PWM modulation schemes do not meet mainstream system requirements is in the processing of digital input data streams having various sample rates. These input data streams may have different sample rates, depending upon the type of device that provides the data, as well as the particular design of the device. The input data streams may also use different clock sources that may have slightly different rates or may drift with respect to one another. Existing technologies require a single input sample rate, or multiple fixed, known input rates, and cannot adapt to the different rates at which devices may provide the input data.
Another problem with prior art systems is that, because they do not have a sample rate converter that can generate a local clock signal, they typically regenerate the PWM clock signal from the input data. This regenerated clock signal cannot support the higher performance that is possible with a locally generated clock signal.